The project plans to use the developing Xenopus trigeminal ganglion in a screen for factors involved in regulating the migration of the trigeminal nerve, with the hope of discovering new proteins and mechanisms. 1. Develop an assay based on the growth in a collagen matrix of neurites from a Xenopus trigeminal ganglion explant. Neurite growth will be influenced by factors produced by cocultured Xenopus animal caps previously injected with synthetic RNA. 2. Screen for factors with attracting/repellent activity by expression cloning. Proteins expressed by animal caps injected with pools of RNA derived from a cDNA library will be tested in conditions designed to detect soluble or membrane-bound attractors/repellents. 3. Confirm the actual involvement of the cloned factor(s) in controlling the trigeminal nerve growth. A direct effect on the axons will be determined with in vitro assays involving the expression of the cloned factor by transfected cells in culture. In situ hybridization, a cement gland substitution assay, and transgenic embryos with inducible expression will be used to establish an in vivo role.